Method of filtration



Patented May 30, 1950 UNETED S'E TENT METHOD or FILTRATION poration of Delaware No Drawing. Application April 19, 1946, Serial No. 663,643

1 Claim. 1

The invention relates to an improved method of filtration, and more particularly to the filtration of sand-slime mineral pulp from an alkaline aqueous medium.

Certain ores, particularly elastic or sedimentary types, are composed of fragments or sand particles, united by cementitious material. Upon comminution of such ore, as in dressing operations, a large quantity of the cementitious material is reduced to a pulverulent state effectively stripping it from the sand particles. The addition of water to the comminuted mass forms a slime of the pulverulent cementitious material, and upon still further addition of water, the slime takes on the characteristics of a colloidal dispersion.

The coexistence of sand and slime impedes filtration procedures. In conventional gravity filtration the sand settles rapidly and the more slowly settling slime forms a compact layer on the upper surface of the settled sand thereby hindering further fluid passage. In operations employing commercial filters of the disc or drum type, the settled sand impedes or halts motion of the filter sector and, as the supernatant liquid is drawn ofi, the suspended slimes clog the filter pores rendering continued filtration difiicult or impossible.

It is known that particles in colloidal dispersion possess an electric charge, either positive or negative, and that by treatment with certain electrolytes the charge may be neutralized and the particles coagulated and precipitated. In filtration operations, particularly in the washing stage, as the electrolyte is leached from the precipitated solid phase, peptization may occur with the result that the precipitate reverts to its original colloidal condition, and either passes through or clogs the filter pores.

It is an object of the invention to provide a means for fiocculating or coagulating slimes or other colloidally dispersed material in an alkaline aqueous medium to obtain a precipitate amenable to conventional filtration operations.

Another object is to lower the pulp density threshold at which settling of the sand-slime mixture occurs.

A further object is to maintain a uniform distribution of sand and flocculated slimes throughout the filtering operation, thereby increasing the permeability of the resulting filter cake and, in addition, enabling relatively free and uninterrupted movement of the sector of a continuous filter.

The present invention is based upon the dis-' covery that the aforecited objects may be attained by the addition of a small amount of an appropriate amine to a sand-slime mineral pulp in an alkaline aqueous medium. Appropriate amines comprise glyoxalidines having a substituent in the 2-position which is a member of the group consisting of higher alkyl and alkenyl radicals. Amines, particularly suitable for use with the invention, are described in U. S. Patent 2,- 267,965 entitled Hydroxyalkyl glyoxalidines and. U. S. Patent 2,355,837 entitled Substituted glyoxalidines both issued to A. L. Wilson.

Hydroxyalkyl glyoxalidines comprise glyoxalidines having a substituent in the 2-position which is a member of the group consisting of higher alkyl and alkenyl radicals and having a hydroxyalkyl group substituent in the l-position. An example is l-l1ydroXyethyl-2-heptadecenyl glyoxalidine (or imidizol-l ethanol-2 heptadecene 8)- which compound is among those used to illustrate the invention.

Substitued glyoxalidines comprise glyoxalidines having a substituent in the 2-position which is a member of the group consisting of the higher alkyl and alkenyl radicals and having a substituent in the 1-position containing an amino group. Examples are l-aminoethyl-Z-heptadecenyl glyoxalidine (or imidizol-l ethylamine-Z heptadecene 8) ethylene) 2-heptadecenyl glyoxalidine (or imidizol-l ethyl amido ethyl amido ethyl amine-2 heptadecene 8) which compounds are among those used to illustrate the invention.

Data from tests illustrating the effectiveness of the invention are given in Table I. The tests show the relative buoyancy imparted to the slimes by the amines, the term buoyancy referring to the apparent property of the flocculated slimes to support the sand particles and maintain them in uniform dispersion in the alkaline aqueous medium. Comparative filtration times and the condition of the resulting filter cake are also shown.

In each of these tests a ten kilogram sample of raw ore of the sand-slime character was digested with grams of sodium carbonate in 5.4 kg. of water for one hour at a temperature of 113 C. and under a steam pressure of 0.70 kg. per sq. cm. (10 lbs. per sq. in.). The digested pulp was then diluted to 50% solids and a 290 gram sample (dry ore basis) removed for test. Each sample was treated with a 1% solution of the hydrochloride of the indicated amine in an amount equal to two pounds per ton (2000 pounds) of ore and l-(aminoethyl diimino on a dry solid basis. The treated pulp was then increased, but notwithstanding this increase, was filtered onaBuchner funnel. considerably below the average washing rate in Table I Amine Added Buoyancy f ff n Segregated. r Imidi'zol-l ethanol-2 Heptadecene 8 -L Fair. 3. Imidizol-l ethylamine-Z Heptadecene 8 Good. 4 linlidizol-l ethyl amido ethyl amide ethyl amine-2 heptae V Do.

ecene 8. Diethylaminoethyl laurate Poor 5.00 Segregated.

1 As 1% solution of the hydrochloride oi the amine. Ratio of. quantity of amine to material being treated (dry solid equvalent) was 1:1000.

In the table, Example 1 had no amine treat- Examples 3 and 4which were treated with amines ment, Example 5 was treated with an amine. not according to the invention. in the class employed in the invention, and Ex- Often desirable mineral values dissolved in the amples 2, 3 and 4 were treated in accordance with aqueous medium associated with a sand-slime the invention with glyoxalidines having a substi 20. pulp. To recover these values by filtration retuent in the 2-position which is a member of the quires a uniform suspension of sand and slime. group, consisting. of higher alkyl and alkenyl radi- Such a suspension is clifficult. to maintain asdicals. In Examples 1 and 5, bouyancy was poor lution-leadsto rapid segregation of the sand. For.v andthc filter cakes.- segregated; whereas in Exexample, a digested pulp of the sand-slime type amples 2; 3 and 4, made according to the invenwas adjusted to 75% solids at which concentration; the. buoyancy was entirely satisfactory and tion the pulp remained in, uniform suspension the filter cakes were uniform and porous. In in; the aqueous medium. Dilution to. 56% solids, addition, the filtering time in Examples 2, 3 and however, led to a rapid segregation oi sands, 4 was considerably faster than in Examples 1 thus. increasing the difiiculties. of filtration op and 5. r erations. Treatment of this same pulp with an Diethylaminoet'hyl laurate used in Example 5, amine, according to the invention, made possiisunsatisfactory as a filter aid in the treatment ble dilution to 50% or lesssolids without disturb.- of: sand-slimev pulp in an alkaline aqueous meing' in anyway the uniform quality of; the sanddium. However, this amine and others of' slime suspension.

the-class; comprising tertiary amino alcohols and The ability to lower the settling threshold of their. fatty acid esters are most satisfactory as sand-slime pulp and; maintain a uniform suspenfilter aids the treatment of sand-slime pulp sion at lower pulp concentrations, made possible in. neutral orslightly acid solutions and such by. the invention, has definite economic value.

treatment with. these amines is the subject of'an- For example, with a pulp containing solids, other i-nyention disclosed in a copending applie 4-0 a recovery of 97% of the-soluble mineral values. cationserial No. 663,644. was accomplished. in four repulpings, whereas, The present invention has. particular eflicacy witha-pulprcontaining 75% solids, sevenrepulpgin converting pulp, which from practical; con.- ingsv were necessary to,effect,thesamerecovery. siderations, is substantially unfilterable and unit-is to be understood that the invention isnot washable, to a condition readily amenable to -e-.- limited, to or by the compositionsof; the sandfiltration treatments. This. is demonstrated by slime materials set forthin this specification, but. examples, the data of which are contained in is applicable to, the treatment of a numberof 'ljable IL In each, example a quantity; of pulp other materials. of like. character wherein, the from a, soda ash digestion of vanadiumv ore was particle size may range from colloidal dimensions adllistdto 50% solids by the addition of Water 50 tothe dimensionsof common sand. Itis also to cQI-itaining the indicated amine, and then filtered be; understood; that; the term "amine" as used-in onaBuchner funnel. Thepulp, after filtration, this application; includes; salts: of. theamine, as containing about'80% solids, was washed by disfor-example, the, hydrochloride, sulphate, or aceplacement with water. until free from soluble matate of the amine, in fact. when. the water soluterial. bility of the aminasalt is. greater than that of Table II Compara- Filtration Av. washing i Amine Added tive 1 Setratc'inrate in ---P ling Value (la/min. ccjmin.

1". None 7 24. 251a 1.5 2 None-washings with 3% sodium carbonate solution 27 23.5 4. 8 3; Imidizol-l ethanol-2 hcptadecene 8 3 lbs/ton 68-. 61.0 8; 1 4.; Imidizol-l ethylaminc-2 heptadecene 8 1 lb./ton 62: 52.5 8.6

Volume of clear liquor in centimeters after 15. min. settling time In the table, Examples 3 and 4, made accordthe aminethesalt may be preferred. Thaining to. the invention, had settling values and vention has a wide range of applicability in the filtration rates over 100% greater than either filtration art and is. not tobe construed as lim- Examples 1 or 2 in which no amine was used. 7 itedto the examples given or their specific mode- The average washing rate in Example 1 was exof operation. For example, the ratio of quantity tremely low due, probably, to loss of electrolyte of amine to material being treated (dry solid (soda ash) in the washing procedure. In Exequivalent) was 121000 in the cited examples.

ample 2, wherein electrolyte was introduced with This-is notto be construed as a necessary lower the washing water, theaveragewashing rate was limit; The quantity of amine to'be-useddepends to a large extent on the nature of the sand-slime pulp and with many mineral pulps of this character a smaller quantity of amine may be effective in improving filtration rates.

What is claimed is:

Method of preventing the formation of a segregated impervious layer of pulverant cementitious material when filter washing a sand-slime mineral pulp in an alkaline aqueous medium, comprising adding to said aqueous medium a glyoxalidine having a substituent in the 2-position which is a member of the group consisting of higher alkyl and alkenyl radicals in an amount equal to about two pounds of said glyoxalidine to each ton (2000 pounds), dry solid basis, of solids present in said aqueous medium; agitating said aqueous medium until a. uniform suspension of sand and slime is produced; withdrawing a portion of said aqueous medium to produce a percmeable mass of uniformly intermixed sand and slime; and thereafter filter-washing said permeable mass of sand and slime to remove soluble material therefrom.

MICHAEL CAROSELLA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

